The invention relates to a method for determining the course over time of the radiation intensity at the location of at least one sample to be examined, which moves in an enclosed sample chamber of a weathering testing device over a circular path of motion about a stationary radiation device for generating UV and global radiation, having at least one sensor detecting the instantaneous radiation intensity of the radiation device, which sensor, together with the at least one sample and offset from it relative to the radiation device, for example offset in the circumferential direction of the path of motion, moves substantially along the path of motion, and an electrical measurement signal corresponding to the instantaneous radiation intensity is derived by the sensor at intervals over time. The invention also relates to a device used to perform this method.
Weathering testing devices are used to test the lightfastness and aging of arbitrary samples, which are distributed over a circular path of motion in the enclosed sample chamber and move around the stationary radiation device. Rain bars or other stationary equipment elements can also be provided in the weathering testing device to allow examination of specimens taking the required ambient conditions into account. As a result, the radiation path from the radiation device to the samples and to the sensor moved along with the samples is repeatedly interrupted or interfered with by stationary obstacles presented by the equipment. In the known devices, the course over time of the radiation intensity is ascertained by making practically individual snapshots of the radiation intensity at comparatively long time intervals or at isolated circumferential positions along the path of motion. It is accordingly impossible to estimate how the equipment-dictated unavoidable interruptions of radiation will affect the measurement error in detecting the radiation intensity. Accordingly it is certainly possible that the radiation interruptions will repeatedly arrive at unfavorable rotational positions of the sensor around the radiation device, causing considerable measurement error with regard to the radiation sent to the samples.
The object of the present invention is to embody a method and a device of the generic type in question such that while avoiding the above disadvantages, more-reliable detection of the course over time of the radiation intensity at the location of the sample is possible. Individual stationary obstacles presented by the equipment to the radiation should have practically no further effect of adulterating the outcome. The method should also be well-suited to industrial realization using current- or energy-saving circuit components, such as for battery and rechargeable battery operation of a device functioning accordingly.
For attaining this object, the measurement signal is integrated in analog fashion in accordance with a first, adjustable timing code with relatively short code intervals at least once in each of these short code intervals via a certain integration interval of adjustable chronological length; that the thus-obtained analog-integrated measurement values of each short code interval are digitized; that the digitized measurement values of a plurality of successive code intervals of the first timing code are arithmetically added and averaged in accordance with a second, adjustable timing code with comparatively longer code intervals, in each of these longer code intervals; and that the thus-obtained arithmetically added, averaged measurement values are stored in memory digitally in a manner capable of chronological association and capable of being called up.
In this method, the influence of individual stationary obstacles to radiation presented by the equipment on the outcome of measurement is practically precluded, since in the analog integration operations, repeated at rapid time intervals, with chronologically long-lasting integration intervals and ensuing addition and averaging of a plurality of individual outcomes, instantaneous situations unfavorable from a radiation standpoint are dropped from the outcome or practically fail to arise. Because of the relatively brief integration intervals with ensuing digitization and digital further processing and storage in memory, the method is very well-suited for a relatively simple, inexpensive practical embodiment, such as for battery and rechargeable battery operation, and thus for mobile use of suitably operating devices using economical circuit components available on the market. Furthermore, for non- battery operation, the influence of possible fluctuations or breakdowns in mains voltage on the outcome of measurement is largely suppressed.
Only the arithmetically added and averaged measurement values are stored in memory for longer, the course over time of the radiation intensity can also be detected over a longer period of time without major expense for memory.
The particularly randomly controlled shifting of the integration intervals lead to a further improvement in the reliability of the method, since the influence of existing interference variables that have the same effect and are thus added together is avoided even more. This is true both for the influence of obstacles to radiation and the influence of mains disruptions.
To attain the stated object, a device suitable for performing the method, is distinguished according to the invention by connecting to the output of the sensor 20, 22 a clocked analog integrator 26, which in analog fashion integrates the measurement signal, in accordance with a first, adjustable timing code with relatively short code intervals a at least once in each of these short code intervals, via a certain integration interval c of adjustable chronological length; display device 34. A microprocessor 36 controls the individual components of the device and can, as in the present case, be linked with an random generator 38.
This device, with a comparatively simple and inexpensive construction, allows easy practical realization of the method of the invention using structural components available on the market.
The timing pulses can be adjusted and adapted to applicable operating conditions. The clock generator always assures correctly timed operation of the individual components of the device that are affected by it. Thus the use of a microprocessor is proved to be especially favorable, especially since a microprocessor is both commercially available and inexpensive and operates in an energy-saving way. The microprocessor can then control the entire course of operation of the device.
One embodiment enables temporary, incrementally renewable storage in memory of information corresponding to the course over time of the radiation intensity.
The integration intervals can be shifted under random control to further suppress error.